The present invention relates to a semiconductor laser drive device and, more particularly, to an APC (automatic power control) for controlling a drive current to obtain a desired output level of the semiconductor laser.
Semiconductor lasers generally have variations in characteristics from one to another and furthermore each laser exhibits deterioration in output characteristics over time. In order to obtain a desired output intensity of a semiconductor laser, an APC circuit is indispensable. Conventional APC circuits detect the output intensity of the semiconductor laser, compare the detected intensity with a desired intensity, and feed back the comparison results to the drive circuit in order to make the drive current match the output intensity with the desired intensity. Such conventional APC circuits always start APC from a drive current of 0. Therefore, it takes extra time to stabilize the drive current. This is significant particularly when the optical output must be modulated in accordance with write data, e.g., when the semiconductor laser is utilized for writing data on an optical disk, thereby disabling high-speed writing.
It has also been desired to detect the remaining service life of a semiconductor laser which changes due to the deterioration over time. Conventionally, a reference value of the drive current is predetermined based on the specifications, and the drive current set by the APC is compared therewith to detect the remaining service life of the semiconductor laser. However, the reference value is set with a relatively large margin in view of variations in characteristics of individual semiconductor lasers. As a result, in some cases the service life is not determined until it is exhausted, and cannot be determined beforehand.